The first generation began around 1950 with the introduction of commercial computers manufactured and sold in quantity. Computers of the first generation stored their programs internally and used the vacuum tubes as their switching technology, but beyond that had little else in common. Each design used a different mix of registers addressing schemes, and instruction sets. The creates variation was found in the devices used for memory, and this affected the logic of the processor design. Each memory technology had some sort of technical drawback, thus giving rise to a variety of machines that favored one design approach over another.

The reports describing the Institute for Advanced Study computer, written by Arthur Burks, Herman Goldstine, and John von Neumann, emphasized the advantages of a parallel memory device that could read and write a full word at a time. But the device that could read and write a full word at a time. But the device they favored, the RCA Selectron tube, took longer than expected to appear; only the RAND Corporation's Johniac used it. America's first commercial machine, the UNIIVAC used a mercury delay line to which words were read and written one bit at a time. The fastest machines used cathode-ray tubes, which were capable of parallel operation. But in practice these tubes, originally intended of other commercial applications, were notoriously unreliable. By far the most popular memory technique for first generation machines was the rotating magnetic drum. An electromechanical device, it was slow, but its reliability and low cost made it suitable for small-scale machines like the IBM 650, Bendix G-15, Alwac III-E, and Librascope LGP-30.

By the end of this period, machines were introduced that incorporated magnetic core memory. With the advent of ferrite cores - and techniques for manufacturing and assembling them in large quantities -- the memory problem endemic to the first generation was effectively solved.

The UNIVAC was designed by J. Presper Eckert and John Mauchly, and first delivered in 1951 (by which time their company had been acquired by Remington Rand). It was the first American computer to be serially produced and sold to commercial customers. Eventually, over 40 were built. Customers included the U.S. Census Bureau, and the Lawrence Livermore Laboratory, the U.S. Army and Air Force, and the General Electric Corporation. Most customers used the UNIVAC for accounting, statistical, and other applications that would later fall under the term data processing.

The computer used serial, binary-coded decimal arithmetic performed in four general-purpose accumulators. Word length was 45 bits; each word could represent 11 binary-coded decimal (BCD) digits plus a sign, or 6 alphabetic characters (6 bits per character plus 1 parity bit). Basic clock speed was 2.25 MHz, and the multiplication time was about 2 msec. Mercury delay-lines stored 1,000 words in high speed memory, while magnetic tape units stored up to 1 million characters on reels of 1/2 inch wide metal tape.

The UNIVAC was ruggedly designed and built. Its central processor contained over 5,000 tubes, installed in cabinets that were arranged in a 10-foot X 14-foot rectangle. Inside this rectangle were placed the mercury delay line tanks. Many design features that later became commonplace first appeared with the UNIVAC: alphanumeric as well as numeric processing, extra bits for error checking magnetic tapes for bulk memory, and buffers that allowed high-speed data transfer between internal and external memories without CPU intervention.

At the time of UNIVAC's announcement, IBM was not committed to electronic computation and was vigorously marketing its line of punched card calculators and tabulators. But, responding to the competitive threat, IBM introduced two machines, on a par with the UNIVAC, the other more modest.

In 1952, IBM announced the 701 computer, originally called the Defense Calculator after its perceived market. True to that perception, of the 19 models installed, most went to U.S. Defense Department or aerospace customers. Initial rental fees were $15,000 a month; IBM did not sell the machines outright. For primary memory, the machine used IBM-designed Williams tubes that could store up to 4,096 36-bit words. Magnetic oxide-coated plastic for intermediate storage. It could perform about 2,000 multiplications/second, but unlike the UNIVAC, the 701's central processor handled control of the slow input/output facilities directly. At about the same time, IBM also developed a character-oriented machine, the 702, for business customers. These machines began IBM's transition to a company that designed and built large-scale electronic digital computers.

Also, at about the same time, IBM developed a smaller machine that had its origins in proposals for extensions of punched card equipment. In the course of its development, its nature shifted to that of a general-purpose, stored program computer, using a magnetic drum for primary memory. IBM's acquisition of drum memory technology from Engineering Research Associates in 1949 was a key element in this shift. The machine now called the IBM 650, was delivered in 1954, rather late relative to objectives. But it proved to be very successful; eventually, there were over a thousand 650 installations at a rental of about $3,500 per month.

By the time of its announcement, the 650 had to compete with a number of other inexpensive, drum-memory machines. But it outsold them all, partly because of IBM's reputation and existing customer base of punched card users, and partly because the 650 was perceived to be easier to program and more reliable that its competitors. The 650's drum had a faster access time (2.4 msec.) than other drum machines. But that was still slow, a limitation that precluded the use of the drum-based machines for many important applications. Ironically, the 650 had less impact among the business customers for whom it was intended than it had at universities, who were able to acquire the computer at a deep discount. There it frequently became the first machine available to the nascent "computing centers" that were just getting underway in the late 1950's.

Another important first-generation computer was the ERA 1103, developed by Engineering Research Associates, the St. Paul Minnesota firm that Remington-Rand bought in 1952. This machine was gear toward scientific and engineering customers, and thus represented a different design philosophy from Remington-Rand's other large machine, the UNIVAC.

The machine used binary arithmetic, a 36-bit word length, and parallel arithmetic operation. Internal memory (1K words) was supplied by Williams tubes, with an ERA-designed drum for backup. It employed a two-address instruction scheme, with the first six bits of a word used to encode a repertoire of 45 instructions. Arithmetic was performed in an internal 72-bit accumulator.

In late 1954, the company delivered to the National Security Agency and to the National Advisory Committee for Aeronautics an 1103 that employed magnetic core in place of the Williams Tube memory - perhaps the first use of core in a commercial machine. (Core had by that time already been installed in the Whirlwind at M.I.T. and in a few other experimental computers.) Following customer advice, ERA modified the machine's instruction set to include an interrupt facility for its I/O, another first in computer design. Interrupts and core memory were later marketed as standard features of the 1103-A model.

In late 1955, IBM began deliveries of the 36-bit 704, its successor to the scientifically oriented 701. It was the most successful of the large first-generation computers. The 704's most notable features were core memory (initially 4K words, up to 32 K by 1957) and a rich instruction repertoire. In addition, the 704 CPU used hardware floating-point arithmetic and three addressable index registers. Both were major advances over 701. To facilitate the use of floating point, an IBM team led by John Backus developed Fortran. Backus has said that he had not envisioned Fortran's use much beyond the 704, but of course it became and has remained, with Cobol, one of the two most successful programming languages of all time. IBM produced 123 704's between 1955 and 1960.

In January 1957, IBM announced the 709 as a compatible upgrade to the 704, but it did not enjoy the same success. Shortly after it was introduced, it became clear that after a ten-year development phase transistors were finally becoming a practical replacement for vacuum tubes. Indeed, the transistorized Philco Transac S-2000 and Control Data 1604 had already beaten IBM to the punch. IBM quickly withdrew the 709 from the market and replaced it with the transistorized 7090. The new machine was architecturally identical to the 709, so IBM engineers used a 709 to write software for the as-yet-unbuilt 7090. The first delivery of the 7090 in late 1959 marked the beginning of IBM's entry into the solid state era.

The first-generation computers established a beachhead among commercial customers, but even considering the success of the IBM 650, they did little more than that. Punched card accounting equipment still did most of the work for business, while engineering and scientific calculating was done with slide rules, desk calculators, or analog computers. Machines like the ERA 1103 were too big, too expensive, and required too much maintenance to be found anywhere but at the largest aerospace firms or government research laboratories. Many still spoke of the total world market for large computers as being limited to very small numbers, much as one might speak of the demand for practical accelerators or wind tunnels. As reliable magnetic core and transistor technology developed, that perception would change.

The second generation of computing lasted from about 1960 to 1965, and was characterized by the use of discrete transistors for switching elements and coincident-current ferrite core planes for internal memory. In software, this era saw the acceptance of high-level programming languages like Fortran and Cobol, although assembly language programming remained common.

From the perspective of the 1990's, the second generation appears to have been more of a transitional period than a major era in computing. The term "revolution," as applied to the invention of the integrated circuit, obscures the fact that the IC's inventors saw their work as an evolutionary outgrowth of their work in materials, circuits, and packaging pioneered in the discrete transistor era. This evolutionary approach hastened the acceptance of the otherwise exotic technology among computer designers. It was during the transistor era when some of the toughest challenges were faced, especially regarding the serial production of reliable transistors with consistent performance. It took from 1949 to 1959 to bring transistors from the laboratory to commercial production and use in computers. But the basic knowledge gained during that period hastened advent of the IC, which went from invention to commercial use in half that time.

Transistors, replacing vacuum tubes on a one-to-one basis, solved the problems of a tube's reliability, heat, and power consumption. As they solved those problems, they exposed another, which proved to be more fundamental; the complexity of interconnecting many thousands of simple circuits to obtain a system that had reasonable computing power. This tyranny of numbers- brought to the force by transistorized computers- would eventually be solved by the integrated circuit.

The most successful transistorized computer was the IBM 1401, introduced in 1060. Based on an initial concept developed at IBM's laboratory in France, the machine employed a character-oriented, variable-length data field, with one bit of each character code reserved to delimit the end of a field. As with the 650, the 1401's design evolved from a plug wired, punched card calculator to a stored-program, general-purpose computer that utilized magnetic media (tape) as well as punched cards for its I/O. Ferrite cores provided a central memory of from 1,400 to 4,000 characters, while transistorized circuits supported a multiplication speed of about 500 numbers/sec.

IBM engineers took pains to make the machine easy to program, especially by those who were comfortable with punched card tabulators, but who know nothing of stored program computers. A simple language call "Report Program Generator" (RPG facilitated processing and printing of tabular data much as punched card equipment was formerly used to perform those tasks. With the 1401, IBM also introduced the Type 1403 printer, a rugged and fast printer that carried type on a moving chain. The system's relatively small size meant that a customer could install it in the same room that was already used from punched card accounting equipment. This combination of features, renting at $2,500 a month for a base system, made the 1401 attractive to many small- and medium- sized businesses.

Eventually, over 10,000 1401's were installed - ten times as many as the 650. Its success marked the ascendancy of IBM over UNIVAC as the dominant computer supplier. Not only did the 1401 broaden the base of potential customers; it finally dispelled lingering doubts over whether the world could absorb more than a small number of electronic computers. Together with the 650, the 1401 made a forceful argument for general-purpose designs. Concurrently with the 1401, IBM also offered the 1620, a like-sized machine intended for scientific applications. Meanwhile, in 1962 the company introduced the 7094, an upgrade to the 7090. It, too, sold well and became the standard large-scale scientific computer of the time.

By the mid-1960's, the IBM Corporation had seized and was vigorously defending a dominant share of the U.S. computer market. Univac, Burroughs, NCR, RCA, Control Data, Philoco/Ford, General Electric. And Honey-well were its chief competitors. Each produced machines that were comparable in price and functionality to the IBM machines, although they had different architectures. By 1070, GE, Ford, and RCA had left the computer business, their places taken by new companies offering computers of a different nature than the classic mainframes of this era.

The second generation was a time when a number of architectural innovations first appeared, but were premature. This is, the features saw only limited use until the next generation, when they became commonplace.

In 1955, Remington Rand Univac contracted with the Lawrence Livermore Laboratory to produce a high-performance computer for weapons design. Design and development of the LARC (Livermore Automatic Research Computer) were beset with problems, but in 1960 the first model complete and accepted by Livermore, with a second model delivered to the Navy's David Taylor Model Basin soon thereafter. The LARC achieved high processing speeds by having a separate processor whose only job was to handle I/O. Logic circuits used Surface Barrier Transistors, developed by Philico in 1955, but already obsolete by 1960. A great deal of effort was spent on packaging the circuits. Getting the backplane wired proved to be a major challenge, ultimately solved by developing special tools that resembled those used by surgeons. The LARC was in impressive performer, but after delivering the two models for a total price of $6 million, Univac stopped production and absorbed a $20 million loss.

At about the same time IBM undertook a similar project called "Stretch," implying that it would dramatically extend the state of the art. Work began in 1956, with the first delivery (to Los Alamos Laboratory) in 1961. Like the LARC, the Stretch introduced a number of innovations in both architecture and device technology. Among the former was its use of a pipelined processor; among the latter was its use of very fast transistors and Emitter-Coupled Logic (ECL). A total of seven other machines, by now called the IBM 7030, were delivered, before the company withdrew the product line. As with Univac's experience with the LARC, IBM absorbed a huge financial loss on the project.

The Atlas computer introduced in 1962 by the British Firm Ferranti, Ltd., employed virtual memory with paging, and provision for multiprogramming. Whereas most first- and second-generation computers had at best only a rudimentary job control facility. Ferranti provided the Atlas with a "Supervisor" program that foreshadowed the operating systems common after 1965.

In 1962, Burroughs introduced the 5000 series of computers that incorporated innovations similar to the Atlas. This series was further designed for optimal execution of programs written in high-level language (Algol). The design of its processor was also novel in its use of a stack-oriented addressing scheme rather than the accumulator-oriented architectures of the first generation. Neither of these two features would prevail in the marketplace, but two others- multiprogramming and virtual memory- would become common a generation later.